The present invention relates to roller finger followers used in overhead cam type internal combustion engines, and more particularly to a roller finger follower wherein a spool-shaped roller set is used.
Roller Finger Followers (RFF) are widely used in overhead cam internal combustion engines to sequentially open and close the cylinder intake and exhaust valves. In a typical application, the RFF serves to transfer and translate rotary motion of a cam shaft lobe into a pivotal motion of the RFF to thereby open and close an associated valve.
It is known that, for a portion of the duty cycle of a typical multiple-cylinder engine, the performance load can be met by a functionally smaller engine having fewer firing cylinders, and that at low-demand times fuel efficiency can be improved if one or more cylinders of a larger engine can be withdrawn from firing service. It is also known that at times of low torque demand, valves may be opened to only a low lift position to conserve fuel, and that at times of high torque demand, the valves may be opened wider to a high lift position to admit more fuel. It is known in the art to accomplish this by de-activating a portion of the valve train associated with pre-selected cylinders in any of various ways. One way is by providing a special two-step RFF having an activatable/deactivatable central slider arm which may be positioned for contact with a high lift lobe of the cam shaft. Such a two-step RFF typically is also configured with rollers disposed at each side of the slider arm for contact with low lift lobes of the cam shaft. Thus, the two-step RFF causes low lift of the associated valve when the slider arm of the RFF is in a deactivated position, and high lift of the associated valve when the slider arm of the RFF is in an activated position to engage the high lift lobe of the cam shaft.
A two-step RFF known in the art comprises a generally elongate body having a pallet end in contact with an axially movable valve stem and an opposing socket end in contact with a stationary pivot such as, for example, a hydraulic lash adjuster (HLA). A moveable and therefore deactivatable high lift slider is positioned central to the RFF body. Rollers are rotatably mounted on each side of the slider on a non-rotatable shaft fixed to the body. The rollers ride on narrow bearings, as for example needle bearings. End washers are used to rotatably fix the rollers and bearings to the shaft and to restrain the rollers and bearings from moving laterally on the shaft.
The width of the bearings in the background art is limited to the width of the rollers themselves. Further, because the bearings are disposed outside the body side walls, the bearings are substantially shielded from flow of lubricating oil within the RFF body.
It is a principal object of the present invention to provide an improved roller bearing arrangement for better durability without substantially increasing the overall width of the RFF.
It is also an object of the invention to provide a simplified RFF having fewer components.
While this invention is described in the context of a two-step deactivation RFF, it should be understood that the bearing improvements may be applied to the rollers of single-step RFFs as well.
Briefly described, a roller finger follower for use in conjunction with a cam shaft of an internal combustion engine comprises an elongate body having first and second side members defining coaxially disposed shaft orifices. A pallet end and a socket end interconnect with the first and second side members to define a slider arm aperture and a latch pin channel. The socket end is adapted to mate with a mounting element such as an hydraulic lash adjuster, and the pallet end is adapted to mate with a valve stem, pintle, lifter, or the like. A slider arm for engaging a high-lift cam lobe is disposed in the slider arm aperture and has first and second ends, the first end of the slider arm being pivotally mounted to the pallet end of the body and the second end defining a slider tip for engaging an activation/deactivation latch. The latch is slidably and at least partially disposed in the latch pin channel, the latch pin having a nose section for selectively engaging the slider tip. A spool-shaped roller comprising a shaft and at least one roller element fixedly attached to the shaft is rotatably disposed in the shaft orifices, the roller being adapted to follow the surface motion of a low-lift cam lobe. Preferably, the shaft is journalled in roller or needle bearings which extend between and through both the first and second shaft orifices, being thus exposed to normal copious oil flow through central regions of the RFF.